1. Technical Field
The present invention relates to a motion sensor for detecting angular velocities and accelerations.
2. Related Art
In the past, three-axis acceleration sensors for detecting accelerations in three axes, namely X, Y, and Z axes utilizing capacitances have been used (see, for example, JP-A-4-299227 (first patent document)). Further, angular velocity sensors for detecting angular velocities utilizing capacitances have similarly been used in the past (see, for example, JP-A-10-227644 (second patent document)).
In resent years, motion sensors such as acceleration sensors capable of detecting accelerations or angular velocity sensors capable of detecting angular velocities have been used for, for example, detecting hand tremor of digital cameras, and have increased in demands therefor. In particular, small-sized motion sensors are in high demand, and motion sensors utilizing capacitances attract attention as the motion sensors which can be downsized and are simple in structure.
In general, the motion sensors utilizing capacitances each have a plumb section as a moving electrode movably supported by beam sections having elasticity and a fixed electrode section distant from the plumb section, thus detecting the acceleration acting on the plumb section by detecting the displacement of the plumb section by the fixed electrode section.
Further, in recent days, five-axis motion sensors (hereinafter referred to as “five-axis motion sensors”) capable of simultaneously detecting accelerations in directions of three axes, namely X, Y, and Z axes and angular velocities of two axes have been proposed (see, for example, JP-A-2004-144598 (third patent document)). In particular, the five-axis motion sensor disclosed in “5-Axis Motion Sensor with SOI Structure Using Resonant Drive and Non-Resonant Detection Mode” in the proceedings of “The 21st Sensor Symposium on Sensors, Micromachine and Applied Systems,” pp. 379-383 (first non-patent document) has a structure which can easily be evacuated inside thereof containing a vibrator, and in addition, has an advantage of being formed by an etching process.
Specifically, the penta-axial motion sensor of the first non-patent document is provided with the vibrator (the plumb section), as the moving electrode movably supported by the beam sections having elasticity, formed between a lower glass substrate having first electrode sections and an upper glass substrate having second electrode sections using an intermediate substrate of a three-layered structure composed of a first conductive layer, an insulating layer, and a second conductive layer, and detects the displacement of the vibrator by the first and second electrodes, thus detecting the acceleration and the angular velocity acting on the vibrator.
Further, the inside of the motion sensor containing the vibrator can easily be evacuated by anodically bonding the upper glass substrate and the lower glass substrate respectively with the intermediate substrate including the vibrator. In addition, since it is sufficient to keep the vibrator formed of the intermediate substrate with predetermined distances from the upper and lower glass substrates, it becomes possible to form the five-axis motion sensor by an etching process.
Hereinafter, the structure of the five-axis motion sensor according to the first non-patent document will more specifically be described. FIG. 20 is a diagram showing the structure of the five-axis motion sensor 100 of the related art.
As shown in FIG. 20, the five-axis motion sensor 100 of the related art is composed of a lower substrate 200 having first electrode sections 201, an upper substrate 400 having second electrode sections 401, and an intermediate substrate 300 formed between the lower substrate 200 made of glass and the upper substrate 400 also made of glass, and a vibrator (the plumb section) 302 as the moving electrode movably supported by elastic beam sections 301, a support section 303 for supporting the beam sections 301, and conducting sections 304a through 304e each for extracting the first electrode sections 201 to the upper substrate 400 are formed using the intermediate substrate 300.
It should be noted here that a so-called silicon-on-insulator (SOI) substrate composed of a first conductive layer 320 formed of a silicon conductive layer, an insulating layer 321 formed of a silicon oxide insulating layer (SiO2), and a second conductive layer 322 formed of a silicon conductive layer is used as the intermediate substrate 300.
The first electrode sections 201 are provided with a plurality of fixed electrodes 210a through 210d for detecting the displacement of the vibrator 302 and a drive electrode 210e for moving the vibrator 302 disposed on the inside surface 220 of the lower substrate 200.
Further, the second electrode sections 401 are provided with a plurality of fixed electrodes 410a through 410d for detecting the displacement of the vibrator 302 and a drive electrode 410e for moving the vibrator 302 disposed on the inside surface 420 of the upper substrate 400.
Still further, each of the electrodes 210a through 210e of the first electrode sections is provided with a wiring extracted to the upper substrate 400 through the intermediate substrate 300. Specifically, a plurality of conducting sections 304a through 304e for respectively extracting the electrodes 210a through 210e from the lower substrate 200 to the upper substrate 400 is formed between the lower substrate 200 and the upper substrate 400 with the intermediate substrate 300.
The upper substrate 400 is provided with through holes 415a through 415j formed from the inside surface 420 to the outside surface 430 thereof, wherein the through holes 415a through 415e are connected to the conducting sections 304a through 304e for extracting the electrodes 210a through 210e of the lower substrate 200, respectively. Further, the through holes 415f through 415j are respectively connected to the electrodes 410a through 410e of the upper substrate 400.
As described above, the five-axis motion sensor 100 has the detection electrodes 210a through 210d, 410a through 410d, and the drive electrodes 210e and 410e extracted to electrodes (not shown) formed on the outside surface 430 of the upper substrate 400.
It should be noted that the vibrator 302 and the conducting sections 304a through 304e are formed separated from each other to be physically insulated for maintaining electrical effects.
Since the vibrator 302 is arranged to face each of the detection electrodes 210a through 210d and 410a through 410d with a predetermined gap, capacitors C101 through C108 (not shown; the capacitors C101 through C104 are formed between the detection electrodes 210a through 210d and vibrator 302, the capacitors C105 through C108 are formed between the detection electrodes 410a through 410d and the vibrator 302, respectively) are formed. Then, the capacitances of the capacitors C101 through C108 vary in response to the displacement of the vibrator 302. Therefore, the displacement of the vibrator 302 can be detected by detecting the capacitances of the capacitors C101 through C108.
The operation of the five-axis motion sensor 100 thus configured as described above will specifically be explained with reference to the drawings. FIGS. 21A and 21B, which are cross-sectional views along the AA-BB line shown in FIG. 20, are diagrams for explaining the principle of detecting accelerations and angular velocities in the five-axis motion sensor 100. It should be noted that the Y-axis direction is assumed to be perpendicular to the drawing sheet.
The drive electrodes 210e and 410e of the five-axis motion sensor 100 are supplied with alternating voltages having phases reversed from each other. The frequency of each of the alternating voltages is the resonant frequency of the vibrator 302, and the vibrator 302 oscillates in the Z-axis direction of FIG. 20 in the resonant frequency.
When acceleration is caused in the Z-axis direction in the vibrator 302, force Fz is caused along the Z-axis direction as shown in FIG. 21A to move the vibrator. When the vibrator is thus moved along the Z-axis, the distances between the electrodes 210a through 210d and the vibrator 302 are enlarged while reducing the capacitances of the capacitors C105 through C108. Further, the distances between the electrodes 410a through 410d and the vibrator 302 are reduced while increasing the capacitances of the capacitors C101 through C104.
Still further, when acceleration is caused in the Y-axis direction, force Fy is caused to make the vibrator 302 incline as shown in FIG. 21B. When the vibrator is thus moved along the Y-axis, the distances between the electrodes 210a, 210d, 410a, and 410d and the vibrator 302 are reduced while increasing the capacitances of the capacitors C101, C104, C105, and C108. Further, the distances between the electrodes 210b, 210c, 410b, and 410c and the vibrator 302 are enlarged while reducing the capacitances of the capacitors C102, C103, C106, and C107.
Therefore, the displacement of the vibrator 302 can be detected by detecting the capacitances of the capacitors C101 through C108, and as a result, the acceleration caused in the vibrator 302 can be detected.
Further, in the vibrator 302, the angular velocity around the Y-axis can be detected by detecting the Coriolis force acting in the X-axis direction, and the angular velocity around the X-axis can be detected by detecting the Coriolis force acting in the Y-axis direction. The Coriolis force can be detected by detecting the displacement of the vibrator 302 similarly to the case of detection of the acceleration, and detection of the Coriolis force acting on the X-axis direction, for example, can be performed by detecting the displacement of the vibrator 302 in the X-axis direction.
Further, the five-axis motion sensor 100 can be manufactured by the following manufacturing method. FIGS. 22A through 22E are diagrams for explaining the manufacturing process of the five-axis motion sensor 100 of the related art.
As shown in FIG. 22A, the intermediate substrate 300 composed of a first conductive layer 320, an insulating layer 321, and a second conductive layer 322 is provided with dimples 330 formed by the insulating materials, and is further provided with openings for connecting sections 331 for establishing conduction between the first conductive layer 320 and the second conductive layer 322 formed by etching.
Subsequently, as shown in FIG. 22B, deep reactive ion etching (DRIE) is performed on the first conductive layer 320 to form a lower area 302-1 of the vibrator 302, a lower area 303-1 of the support section 303, and lower areas 304a-1 through 304e-1 of the conducting sections 304a through 304e separately from each other. Further, the conducting sections 304a through 304e are provided with the connecting sections 331 for respectively connecting the lower areas 304a-1 through 304e-1 and the upper areas 304a-2 through 304e-2 with conductive materials.
After then, as shown in FIG. 22C, the lower substrate 200 previously provided with a dimple sections 202 and the first electrode sections 201 is provided, and the first conductive layer 320 of the intermediate substrate 300 is anodically bonded with the inner surface of the lower substrate 200.
Further, as shown in FIG. 22D, DRIE is performed on the second conductive layer 322 to form the beam sections 301, an upper area 302-2 of the vibrator 302, an upper area 303-2 of the support section 303, and upper areas 304a-2 through 304e-2 of the conducting sections 304a through 304e. 
In this case, DRIE is performed on the second conductive layer 322 so that connections are provided between the upper area 302-2 of the vibrator 302 and the beam sections 301, and between the beam sections 301 and the upper area 303-2 of the support section 303, and also the upper area 302-2 of the vibrator 302 is disposed above the lower area 302-1 of the vibrator 302, the upper area 303-2 of the support section 303 is disposed above the lower area 303-1 of the support section 303, and the upper areas 304a-2 through 304e-2 of the conducting sections 304a through 304e are respectively disposed above the lower areas 304a-1 through 304e-1 of the conducting sections 304a through 304e. 
Further, as shown in FIG. 22E, the upper substrate 400 previously provided with the second electrode sections 401 and so on is prepared, and the intermediate substrate 300 and the upper substrate 400 are anodically bonded with each other so that the inside surface 430 of the upper substrate 400 faces the upper surface of the intermediate substrate 300.